Comorbidity: Addiction and Other Mental Illnesses

How common are comorbid drug use and other mental disorders?

Many people who regularly abuse drugs are also diagnosed with mental disorders and vice versa. The high prevalence of this comorbidity has been documented in multiple national population surveys since the 1980s. Data show that persons diagnosed with mood or anxiety disorders are about twice as likely to suffer also from a drug use disorder (abuse or dependence) compared with respondents in general. The same is true for those diagnosed with an antisocial syndrome, such as antisocial personality or conduct disorder. Similarly, persons diagnosed with drug disorders are roughly twice as likely to suffer also from mood and anxiety disorders (see "Overlapping Conditions–Shared Vulnerability").

Gender is also a factor in the specific patterns of observed comorbidities. For example, the overall rates of abuse and dependence for most drugs tend to be higher among males than females. Further, males are more likely to suffer from antisocial personality disorder, while women have higher rates of mood and anxiety disorders, all of which are risk factors for substance abuse.

Childhood ADHD and Later Drug Problems

Numerous studies have documented an increased risk for drug use disorders in youth with untreated ADHD, although some suggest that only a subset of these individuals are vulnerable: those with comorbid conduct disorders. Given this linkage, it is important to determine whether effective treatment of ADHD could prevent subsequent drug abuse and associated behavioral problems. Treatment of childhood ADHD with stimulant medications such as methylphenidate or amphetamine reduces the impulsive behavior, fidgeting, and inability to concentrate that characterize ADHD. Yet, some physicians and parents have expressed concern that treating childhood ADHD with stimulants might increase a child's vulnerability to drug abuse later in life. Recent reviews of long-term studies of children with ADHD who were treated with stimulant medications (e.g., Adderal, Ritalin, Concerta) found no evidence for this increase. However, most of these studies have methodological limitations, including small sample sizes and nonrandomized study designs, indicating that more research is needed, particularly with adolescents.